JP2706271B2 - Discharge lamp lighting device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device for lighting a discharge lamp such as a fluorescent lamp, and more particularly to exhaustion of a filament emitter at the end of the life of a discharge lamp, breakage of a filament, and the like. It relates to the detection of abnormalities in

[Conventional technology]

As is well known, a discharge lamp such as a fluorescent lamp causes a half-wave discharge phenomenon at the end of life. This half-wave discharge phenomenon means that the amount of thermionic emission active material (commonly called emitter) applied to the filament electrode of the discharge lamp decreases, the emitter of one filament electrode is completely eliminated, and thermionic emission from the filament electrode is reduced. In other words, thermoelectrons are emitted only from the other filament electrode, and the device operates as if it were a rectifier.

In such a state, the impedance of the discharge lamp ballast mainly composed of the inductance element decreases. As a result, an overcurrent flows through the discharge lamp ballast and the like, and the heat generation of the discharge lamp ballast and the voltage / current stress increase.
There is a possibility that the reliability is significantly deteriorated.

In order to prevent such a problem, the end of the lamp life is detected by the lamp abnormality detecting means, and the power supplied to the discharge lamp is reduced or stopped to protect the lighting circuit. In particular, in an inverter type discharge lamp ballast using a switching element as a lighting circuit,
In order to reduce the stress of the switching element, the above-mentioned lamp abnormality detecting means is often added.

FIG. 14 shows an example of a conventional discharge lamp lighting device having the lamp abnormality detection circuit as described above.

The discharge lamp lighting device shown in FIG. 14 converts the voltage of the DC power supply E into a high-frequency voltage by alternately turning on the _two switching elements Q ₁ and Q ₂ by the control circuit CR.
This high-frequency voltage is supplied to the discharge lamps FL ₁ , F via the balancer BL _1.
The discharge lamps FL ₁ and FL ₂ are turned on at a high frequency by being applied to L ₂ .

Also, this discharge lamp lighting device has a lamp abnormality detection circuit DT.
_{In 1} , the lamp voltage of the discharge lamp FL ₁ , that is, the voltage at point A (the power supply side electrode terminal of the filament on the balancer BL ₁ side of the discharge lamp FL ₁ ) is detected, and the detected discharge lamp FL _{1 is} detected.
Comparing the lamp voltage with a reference voltage, the filament emitter end of life of the discharge lamp FL ₁ wasting, abnormal when abnormal lamp voltage of the discharge lamp FL ₁ by the occurrence of broken filaments, etc. exceeds the reference voltage rises A signal is generated and given to the control circuit CR. As a result, the control circuit CR enforces blocking the switching elements Q _1, Q ₂ stops switching of the switching elements Q _1, Q ₂ constituting the inverter circuit, thereby protecting the switching element Q _1, Q ₂ .

Similarly, the lamp abnormality in the detection circuit DT _2, the discharge lamp FL ₂ of the lamp voltage, i.e., detects the voltage of the point B (the power supply-side electrode terminals of the discharge lamp FL ₂ balancer BL ₁ side of the filament), the detected discharge lamp The lamp voltage of FL ₂ was compared with the reference voltage, and the lamp voltage of discharge lamp FL ₂ increased and exceeded the reference voltage due to abnormalities such as exhaustion of the filament emitter at the end of the life of discharge lamp FL ₂ and breakage of the filament. Sometimes an abnormal signal is generated and given to the control circuit CR.
As a result, the control circuit CR enforces blocking the switching elements Q _1, Q ₂ stops switching of the switching elements Q _1, Q ₂ constituting the inverter circuit, thereby protecting the switching element Q _1, Q ₂ .

Lamp abnormality detection circuit DT _1, specifically, as shown in FIG. 15, the lamp voltage of the discharge lamp FL _1, i.e. the diode D ₁₁ the voltage V _A at the point A, the resistor R _11, R ₁₂ and capacitor C ₁₁ rectifies, smoothes and divides the voltage, and the rectified, smoothed and divided voltage, that is, the voltage V _C at the point C, is applied to the middle point of the resistor R ₁₃ and the Zener diode ZD ₁₁ by a comparator (comprising an operational amplifier) CP ₁ . The resulting reference voltage is compared.

When the discharge lamp FL ₁ has an abnormality such as exhaustion of the filament emitter at the end of its life or a broken filament, the voltage at point A
When V _A rises, the voltage V _C at point C made by applying a voltage V _A at point A minute also increases, the voltage V _C at point C Zener diode ZD ₁₁
When the reference voltage created by
CP ₁ is to control circuit CR, adapted to provide an error signal.

In FIG. 14, CH ₁ is a choke coil, and C ₁₂ and C
₁₃ and C ₁₄ are capacitors. Also, a lamp abnormality detection circuit
DT ₂ has the same configuration as that of FIG.

[Problems to be solved by the invention]

In such a conventional discharge lamp lighting device, the discharge lamp FL _1, to detect the abnormality of the FL _2, constant discharge lamp FL _1, FL ₂ of the lamp voltage with a ramp abnormality detection circuit DT _1, DT ₂ Therefore, it is necessary to take measures to prevent a malfunction due to a change in lamp voltage when the ambient temperature, the power supply voltage or the like changes, or when dimming is performed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a discharge lamp lighting device capable of detecting a lamp abnormality without being affected by a change in lamp voltage caused by a cause other than the abnormality of the discharge lamp.

[Means for solving the problem]

In the discharge lamp lighting device of the present invention, a discharge lamp is connected to an AC power supply via a discharge lamp ballast, and a voltage dividing impedance element group is connected to the discharge lamp to form first and second voltage dividing circuits. Connecting a potential difference detecting impedance element between the respective middle points of the first and second voltage dividing circuits to form a bridge circuit, and providing a comparison circuit for comparing a potential difference between both ends of the potential difference detecting impedance element with a threshold value It is a thing.

In this case, the first and second voltage dividing circuits are formed as follows.

First, the first voltage dividing circuit is formed by connecting a series circuit of first and second voltage dividing impedance elements in parallel with the first discharge lamp. Further, the second voltage dividing circuit is formed by connecting a series circuit of the third and fourth voltage dividing impedance elements in parallel with the second discharge lamp (first to fifth, seventh, and seventh).
(Eighth embodiment; FIGS. 1 to 6, FIG. 8, and FIG. 9).

Secondly, the first voltage dividing circuit is formed by connecting a series circuit of the first and second voltage dividing impedance elements in parallel with the first discharge lamp. The second voltage dividing circuit is formed by connecting a series circuit of the third and fourth impedance elements for voltage division in parallel with the series circuit of the first and second discharge lamps (sixth embodiment; seventh embodiment). Figure).

Third, the first voltage dividing circuit is formed by connecting a first voltage dividing impedance element to the first discharge lamp in series, and
Is formed by connecting a second impedance element for voltage division to the second discharge lamp in series (ninth and tenth embodiments; FIGS. 10 and 11).

Fourth, a series circuit of the first and second discharge lamps is used as a first voltage dividing circuit, and the second voltage dividing circuit is formed by connecting first and second voltage dividing impedance elements in series.
Example 11; FIG. 12).

Fifth, the first voltage dividing circuit is formed by connecting a first voltage dividing impedance element to the discharge lamp in series, and the second voltage dividing circuit is formed by connecting the second and third voltage dividing impedance elements in series. (Twelfth embodiment; FIG. 13).

[Action]

According to the configuration of the present invention, when the discharge lamp reaches the end of its life and the lamp voltage changes, the bridge circuit including the first and second voltage dividing circuits and the potential difference detecting impedance element changes from the balanced state to the unbalanced state. Accordingly, the potential difference between both ends of the potential difference detecting impedance element connected between the respective middle points of the first and second voltage dividing circuits changes from a state of substantially zero to a state exceeding the threshold value. As a result, a lamp abnormality detection output is generated from the comparison circuit.

On the other hand, voltage fluctuations caused by causes other than abnormality of the discharge lamp have the same effect on the first and second voltage dividing circuits. At this time, since the equilibrium condition of the bridge circuit is not broken, the potential difference between both ends of the potential difference detecting impedance element is The threshold value is not exceeded, and therefore, no lamp abnormality detection output is generated from the comparison circuit.

〔Example〕

A first embodiment of the present invention will be described with reference to FIGS. In this discharge lamp lighting device, as shown in FIGS. 1 and 2, discharge lamps LP ₁ and LP ₂ are connected to an AC power supply 1 via a discharge lamp stabilizer 2, and the voltage dividing impedance elements 3 and 5 are connected. together are connected in parallel a series circuit to the discharge lamp LP ₁ to form a voltage divider circuit BA _1, a voltage dividing circuit BA ₂ are connected in parallel a series circuit to the discharge lamp LP ₂ voltage dividing impedance elements 4,6 A potential difference detecting impedance element 7 is connected between the respective midpoints of the voltage dividing circuits BA ₁ and BA ₂ , and a comparison circuit 8 for comparing the potential difference between both ends of the potential difference detecting impedance element 7 with a threshold value is provided. .

In this case, the discharge lamp ballast 2 includes, for example, a leakage transformer and a balancer.

The voltage dividing circuits BA ₁ and BA ₂ are respectively connected to the discharge lamps LP ₁ and L
A configuration for dividing the lamp voltage P _2, the voltage divider circuit
A bridge circuit is formed by BA ₁ and BA ₂ and the impedance element 7 for detecting a potential difference. Further, each of the voltage dividing impedance elements 3 to 6 constituting the voltage dividing circuits BA ₁ and BA ₂ is composed of, for example, a resistor. When both of the discharge lamps LP ₁ and LP ₂ are normally lit, the bridge circuit is balanced. The resistance value is set so that the potential difference between both ends of the potential difference detecting impedance element 7 becomes substantially zero. The voltage dividing impedance elements 3 to 6 and the potential difference detecting impedance element 7 are not limited to resistors, but may be capacitors or the like.

When the discharge lamp lighting device changes the lamp voltage when _one of the discharge lamps LP ₁ or LP ₂ reaches the end of its life, the voltage divider circuits BA ₁ and BA ₂ and the potential difference detecting impedance element 7 are used.
Changes from an equilibrium state to an unbalanced state, so that the potential difference between both ends of the potential difference detecting impedance element 7 connected between the midpoints of the voltage dividing circuits BA ₁ and BA ₂ changes from a state where the potential difference is substantially zero to a threshold value. Change to a state exceeding. As a result, a lamp abnormality detection output is generated from the comparison circuit 8.

On the other hand, fluctuations in the lamp voltage due to causes other than abnormalities in the discharge lamps LP ₁ and LP ₂ affect the voltage dividing circuits BA ₁ and BA ₂ in the same manner. The potential difference between both ends of the impedance element 7 does not exceed the threshold value, so that the comparison circuit 8 does not generate a lamp abnormality detection output.

Here, the comparison circuit 8 will be described in detail. The comparison circuit 8 includes transistors 9A and 10A having the same characteristics, a diode 11, a capacitor 12, and a resistor 13.

The operation will be described. When both the discharge lamps LP ₁ and LP ₂ are normally lit and the bridge circuit including the voltage dividing impedance elements 3 to 6 and the potential difference detecting impedance element 7 is in an equilibrium state, the potential difference detecting impedance element is used. Since there is no potential difference between both ends of transistor 7, transistor 9
Since no base current flows through A and 10A and the off state is maintained, no voltage appears between terminals a and b.

However, when one of the discharge lamps LP ₁ and LP ₂ reaches the end of its life, the amplitude or phase of the lamp voltage changes, the previous bridge circuit becomes unbalanced, and the potential difference between both ends of the potential difference detecting impedance element 7. Appears. The polarity of this potential difference is reversed depending on which of the discharge lamps LP ₁ and LP ₂ is at the end of its life. When the potential difference reaches a base-emitter voltage V _BE (corresponding to a threshold value) of one of the transistors 9A and 10A according to the polarity, a base current flows through one of the transistors 9A and 10A,
Either 9A or 10A is turned on. As a result, a collector current flows through the voltage dividing impedance elements 3 and 4 and the potential difference detecting impedance element 7 to the turned on one of the transistors 9A and 10A, the capacitor 12 is charged through the diode 11, and the voltage between both ends increases. I do. Therefore, a DC voltage appears between the terminals a and b. This voltage becomes the lamp abnormality detection output. Note that the resistor 13 is for discharging the capacitor 12.

The base-emitter voltage of transistors 9A and 10A
Since V _BE is constant at about 0.7 V, the threshold value for the potential difference of the potential difference detecting impedance element 7 is also 0.7 V. However, since the potential difference can be adjusted by changing the resistance value of the potential difference detecting impedance element 7, the relative The threshold value can be set freely, and there is no problem.

According to the discharge lamp lighting device of this embodiment, the discharge lamp LP
_1, LP ₂ bisection pressure impedance element 3-6 divider circuit BA ₁ by connecting, BA ₂ is formed, connecting the potential difference detection impedance element 7 between each of the voltage dividing circuit BA _1, BA ₂ midpoint Since the comparison circuit 8 is provided for comparing the potential difference between both ends of the potential difference detecting impedance element 7 with a threshold value, fluctuations in lamp voltage caused by causes other than abnormalities of the discharge lamps LP ₁ and LP ₂ , for example, ambient temperature, power supply The lamp abnormality can be detected with high accuracy from the lamp voltage change due to the abnormality at the end of life of the discharge lamps LP ₁ and LP ₂ without being affected by the change in the voltage or the lamp voltage due to dimming.

A second embodiment of the present invention will be described with reference to FIG. This discharge lamp lighting device uses a comparison circuit 8B instead of the comparison circuit 8 in FIG. 2, and the other parts are the same as those in FIG.

The comparison circuit 8B includes transistors 9A and 9A in the comparison circuit 8.
In this embodiment, two comparators 9B and 10B are used instead of 0A, and the operation is the same as that of the comparison circuit 8.

The effect of this embodiment is the same as that of the first embodiment. A third embodiment of the present invention will be described with reference to FIG. This discharge lamp lighting device uses a comparison circuit 8C instead of the comparison circuit 8 in FIG. 2, and the other components are the same as those in FIG.

The comparison circuit 8C includes the transistors 9A, 1
Instead of 0A, diode bridge 9C and comparator 10C
Is used.

In the comparison circuit 8C, the potential difference between both ends of the potential difference detecting impedance element 7 is subjected to full-wave rectification and then compared with a threshold value. Other operations are the same as those of the comparison circuit 8.

 The effect of this embodiment is similar to that of the first embodiment.

A fourth embodiment of the present invention will be described with reference to FIG. This discharge lamp lighting device uses a comparison circuit 8D in place of the comparison circuit 8C in FIG. 4, and the other components are the same as those in FIG.

The comparison circuit 8D is obtained by adding a zener diode 14 to the comparison circuit 8C.

In the comparison circuit 8D, the potential difference between both ends of the potential difference detecting impedance element 7 is full-wave rectified like the comparison circuit 8C, and then compared with a threshold value. It is not the value but the Zener voltage of the Zener diode 14. Other operations are the same as those of the comparison circuit 8.

 The effect of this embodiment is similar to that of the first embodiment.

A fifth embodiment of the present invention will be described with reference to FIG. This discharge lamp lighting device is obtained by applying the present invention to a multi-lamp lighting device. That is, this discharge lamp lighting device has 5
Intended for lighting the discharge lamp LP ₁ ~LP ₅ of the discharge lamp LP _1, the combination of LP _2, the combination of the discharge lamp LP _2, LP _3, discharge lamp LP _3, the combination of LP _4, the discharge lamp LP _4, L
The combination of P _5, FIG. 1, respectively as well as dividing the impedance elements 31, 41, 51, 61; 32, 42, 52, 62; 33, 43,
53, 63; 34, 44, 54, 64 by connecting the voltage dividing circuit _{BA 11, BA 12; BA 21} ,
BA ₂₂ ; BA ₃₁ , BA ₃₂ ; BA ₄₁ , BA ₄₂ are formed respectively, and each voltage dividing circuit BA ₁₁ , BA ₁₂ ; BA ₂₁ , BA ₂₂ ; BA ₃₁ , BA ₃₂ ; BA ₄₁ , BA ₄₂ The potential difference detecting impedance elements 71 to 74 are connected therebetween, thereby forming four bridge circuits, and the potential difference between both ends of each of the potential difference detecting impedance elements 71 to 74 is detected by the comparison circuits 81 to 84, respectively. It is like that.

The specific configurations of the discharge lamp ballast 2 and the comparison circuits 81 to 84 are the same as those in FIG.

In the discharge lamp lighting device, the discharge lamp LP ₁ ~LP ₅
If one or more of the four end circuits reach the end of life, one or more of the four bridge circuits become unbalanced and the terminals a ₁ to
A lamp abnormality detection output is generated from any of a _{4 and} b.

 The effect of this embodiment is similar to that of the first embodiment.

A sixth embodiment of the present invention will be described with reference to FIG. This discharge lamp lighting device is one in which the present invention is applied to a two-lamp serial lighting type. That is, in this discharge lamp lighting device, discharge lamps LP ₁ and LP ₂ are connected in series to an AC power supply 1 via a discharge lamp stabilizer 2, and a series circuit of voltage-dividing impedance elements 3 and 5 composed of resistors is connected to the discharge lamp LP. ₁ to form a voltage dividing circuit BA ₁ and connect a series circuit of voltage dividing impedance elements 4 and 6 consisting of resistors to a discharge lamp L.
A voltage dividing circuit BA ₂ is formed by connecting in parallel to the series circuit of P ₁ and LP ₂ , and a potential difference detecting impedance element 7 composed of a resistor is connected between the respective middle points of the voltage dividing circuits BA ₁ and BA _2. A bridge circuit is formed, and a comparison circuit 8 for comparing a potential difference between both ends of the potential difference detecting impedance element 7 with a threshold value is provided.

This embodiment differs from the first embodiment in that the voltage dividing circuit BA ₁ ,
BA ₂ connections only here, and other configurations are the same as the first embodiment.

Like this discharge lamp lighting device, two discharge lamps LP ₁ ,
When the LP ₂ is lit in series, as shown in FIG.
By connecting A ₁ and BA ₂ , when one of the discharge lamps LP ₁ or LP ₂ reaches the end of its life, the bridge circuit becomes unbalanced, and as a result, a lamp abnormality detection output is generated from the comparison circuit 8. Will do.

 The effect of this embodiment is similar to that of the first embodiment.

A seventh embodiment of the present invention will be described with reference to FIG. The discharge lamp lighting apparatus, in the configuration of FIG. 1, a discharge lamp LP _1, respectively are interposed diode bridge 15 and 16 between the LP ₂ dividing circuit BA _1, BA _2, discharge lamp LP _1, LP _Two
Each of the lamp voltages is subjected to full-wave rectification by diode bridges 15 and 16 and applied to voltage dividing circuits BA ₁ and BA ₂ , and the other components are the same as those in FIG.

In the configuration of FIG. 1 described above, the increase in the amplitude and the phase shift of only the half-wave of the lamp voltage are detected. However, in the configuration of FIG. , The phase shift can be detected, and the detection accuracy of the abnormality can be improved.

Other effects of this embodiment are similar to those of the first embodiment.

An eighth embodiment of the present invention will be described with reference to FIG. This discharge lamp lighting device uses a high frequency inverter type discharge lamp ballast 2A instead of the copper-iron type discharge lamp ballast 2 in the configuration of FIG.

The inverter-type discharge lamp ballast 2A includes a rectifier 21, a smoothing capacitor 22, switching elements 23 and 24, a choke coil 25, capacitors 26 and 27, and a balancer 28.

In this discharge lamp ballast 2A, on / off signals are alternately provided to the switching elements 23 and 24, and based on this, the switching elements 23 and 24 perform a switching operation. The choke coil 25 and the capacitors 26 and 27 form an LC series resonance circuit, accumulate and release energy with the switching operation of the switching elements 23 and 24, and generate a sine wave high-frequency output at both ends of the capacitor 27. Then, the balancer 28 distributes the high frequency output and supplies it to the discharge lamps LP ₁ and LP ₂ .

The abnormality detection operation of the discharge lamps LP ₁ and LP ₂ is described in the first section.
It is the same as that in the figure.

 The effect of this embodiment is similar to that of the first embodiment.

A ninth embodiment of the present invention will be described with reference to FIG. In this discharge lamp lighting device, discharge lamps LP ₁ and LP ₂ are connected to an AC power supply 1 via a discharge lamp ballast ₂ , and the discharge lamp LP ₁
For example a dividing impedance element 3 consisting of resistors to form a connected in series voltage divider circuit BA _3, the discharge lamp LP _2, for example a dividing impedance element 4 comprising resistors connected in series voltage divider circuit BA ₄ Forming and voltage dividing circuit BA ₃ , B
Connect the potential difference detection impedance element 7 to form a bridge circuit between the midpoint of the A _4, in which the potential difference between both ends of the potential difference detecting impedance element 7 provided with a comparator circuit 8 is compared with a threshold value. In this case, the common end of the voltage dividing impedance elements 3 and 4 is connected to one end of the AC power supply 1.

In this embodiment, similarly to the above embodiments, the discharge lamp LP
_1, the bridge circuit both in a normal state of the LP ₂ is is configured to the value of the dividing impedance elements 3 and 4 so as to balance, the discharge lamp LP _1, when one of LP ₂ is end of life bridge The circuit becomes unbalanced and the comparator 8 generates a lamp abnormality detection output.

 The effect of this embodiment is similar to that of the first embodiment.

A tenth embodiment of the present invention will be described with reference to FIG. This discharge lamp lighting device uses a high frequency inverter type discharge lamp ballast 2A instead of the copper-iron type discharge lamp ballast 2 in the configuration of FIG. In this case, the common end of the dividing impedance elements 3 and 4 have been connected to the positive terminal of the smoothing capacitor 22, the voltage dividing circuit BA _3, BA ₄ DC voltage is applied.

 Others are the same as those in FIG.

In addition, regarding the configuration and operation of the discharge lamp ballast 2A,
As described with reference to FIG.

 The effect of this embodiment is similar to that of the first embodiment.

An eleventh embodiment of the present invention will be described with reference to FIG. This discharge lamp lighting device includes a voltage dividing circuit B by connecting discharge lamps LP ₁ and LP ₂ in series to an AC power supply 1 via a discharge lamp ballast 2.
A ₅ and the voltage dividing impedance elements 4, 6
Are connected in series to form a voltage dividing circuit BA ₂ and the voltage dividing circuits BA ₅ and BA ₂
A potential difference detecting impedance element 7 is connected between each of the intermediate points to form a bridge circuit, and a comparison circuit 8 that compares the potential difference between both ends of the potential difference detecting impedance element 7 with a threshold value
Is provided.

Also in this discharge lamp lighting device, when one of the discharge lamps LP ₁ and LP ₂ is abnormal, the bridge circuit becomes unbalanced and the comparator 8 generates a lamp abnormality detection output.

 The effect of this embodiment is similar to that of the first embodiment.

A twelfth embodiment of the present invention will be described with reference to FIG. The discharge lamp lighting device includes an AC power source 1 to the via discharge lamp ballast 2 connected to the discharge lamp LP _1, the discharge lamp LP ₁ binary pressure impedance element 3 are connected in series the voltage dividing circuit BA
₃ to form a, a dividing impedance elements 4 and 6 are connected in series to form a voltage divider circuit BA _2, connect the potential difference detection impedance element 7 between each of the voltage dividing circuit BA _3, BA ₂ midpoint And a comparison circuit 8 for comparing a potential difference between both ends of the potential difference detecting impedance element 7 with a threshold value.

The discharge lamp lighting device, discharge lamp LP suit ₁ characteristic, discharge bridge circuit during normal lamp LP ₁ is to adjust the minutes value of the pressure impedance elements 4, 6 and the potential difference detection impedance element 7 so as to equilibrate There, the discharge lamp LP ₁ becomes abnormal, the bridge circuit comparator circuit 8 becomes unbalanced to generate a lamp abnormality detection output.

 The effect of this embodiment is similar to that of the first embodiment.

〔The invention's effect〕

According to the discharge lamp lighting device of the present invention, the first and second voltage dividing circuits are formed by connecting the voltage dividing impedance element group to the discharge lamp, and each midpoint of the first and second voltage dividing circuits is formed. A potential difference detecting impedance element is connected between the two elements, and a comparator for comparing the potential difference between both ends of the potential difference detecting impedance element with a threshold value is provided. It is possible to detect a lamp abnormality without any trouble.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention;
FIG. 2 is a circuit diagram showing a specific configuration of the circuit of FIG. 1, FIG. 3 is a circuit diagram of a main part showing a configuration of a second embodiment of the present invention,
FIG. 4 is a circuit diagram of a main part showing a configuration of a third embodiment of the present invention, FIG. 5 is a circuit diagram of a main part showing a configuration of a fourth embodiment of the present invention, and FIG. FIG. 7 is a circuit diagram showing a configuration of a fifth embodiment of the present invention, FIG. 7 is a circuit diagram showing a configuration of a sixth embodiment of the present invention, and FIG. 8 is a circuit diagram showing a configuration of a seventh embodiment of the present invention. FIG. 9 is a circuit diagram showing a configuration of an eighth embodiment of the present invention, FIG. 10 is a circuit diagram showing a configuration of a ninth embodiment of the present invention, and FIG. 11 is a tenth embodiment of the present invention. FIG. 12 is a circuit diagram showing a configuration of an eleventh embodiment of the present invention, FIG. 13 is a circuit diagram showing a configuration of a twelfth embodiment of the present invention, and FIG. FIG. 15 is a circuit diagram showing an example of a configuration of a conventional discharge lamp lighting device, and FIG. 15 is a circuit diagram showing a specific configuration of a main part of FIG. 1 ...... AC power source, 2 ...... discharge lamp ballasts, 3-6 ...... partial pressure impedance element, 7 ...... potential difference detection impedance element, 8 ...... comparator circuit, LP _1, LP ₂ ...... discharge lamps, B
A ₁ -BA ₅ …… Division circuit

Claims (6)

(57) [Claims] 1. A discharge lamp is connected to an AC power supply via a discharge lamp ballast, and a voltage dividing impedance element group is connected to the discharge lamp to form first and second voltage dividing circuits. A potential difference detecting impedance element is connected between each of the middle points of the first and second voltage dividing circuits to form a bridge circuit, and a comparison circuit for comparing a potential difference between both ends of the potential difference detecting impedance element with a threshold value is provided. Discharge lamp lighting device. 2. A first and a second discharge lamp are connected to an AC power supply via a discharge lamp ballast, and a series circuit of first and second voltage-dividing impedance elements is connected in parallel with the first discharge lamp. To form a first voltage divider circuit,
A series circuit of third and fourth voltage dividing impedance elements is connected in parallel to the second discharge lamp to form a second voltage dividing circuit, and each midpoint of the first and second voltage dividing circuits is connected. A discharge lamp lighting device comprising a bridge circuit formed by connecting an impedance element for detecting a potential difference therebetween, and a comparison circuit for comparing a potential difference between both ends of the impedance element for detecting a potential difference with a threshold value. 3. A first discharge lamp and a second discharge lamp are connected in series to an AC power supply via a discharge lamp ballast, and a series circuit of first and second voltage dividing impedance elements is connected in parallel to the first discharge lamp. To form a first voltage-dividing circuit, and connect a series circuit of third and fourth voltage-dividing impedance elements in parallel with the series circuit of the first and second discharge lamps to form a second voltage-dividing circuit. A voltage dividing circuit is formed, a potential difference detecting impedance element is connected between each of the middle points of the first and second voltage dividing circuits to form a bridge circuit, and a potential difference between both ends of the potential difference detecting impedance element is formed. A discharge lamp lighting device provided with a comparison circuit for comparing with a threshold value. 4. An AC power source is connected to a first and a second discharge lamp via a discharge lamp ballast, and a first voltage dividing impedance element is connected in series to the first discharge lamp to form a first voltage divider. A second voltage dividing circuit is formed by connecting a second voltage dividing impedance element in series with the second discharge lamp to form a second voltage dividing circuit, and each midpoint of the first and second voltage dividing circuits is formed. A discharge lamp lighting device comprising a bridge circuit formed by connecting an impedance element for detecting a potential difference therebetween, and a comparison circuit for comparing a potential difference between both ends of the impedance element for detecting a potential difference with a threshold value. 5. A first voltage dividing circuit is formed by connecting first and second discharge lamps to an AC power supply via a discharge lamp ballast in series, and the first and second voltage dividing impedance elements are formed. A second voltage dividing circuit is formed in series, a potential difference detecting impedance element is connected between respective middle points of the first and second voltage dividing circuits to form a bridge circuit, and the potential difference detecting impedance is formed. A discharge lamp lighting device provided with a comparison circuit for comparing a potential difference between both ends of an element with a threshold value. 6. A first voltage dividing circuit is formed by connecting a discharge lamp to an AC power supply via a discharge lamp ballast and connecting a first voltage dividing impedance element in series to the discharge lamp. A second voltage dividing circuit is formed by connecting the second and third voltage dividing impedance elements in series, and a potential difference detecting impedance element is connected between respective middle points of the first and second voltage dividing circuits to form a bridge. A discharge lamp lighting device comprising: a circuit; and a comparison circuit for comparing a potential difference between both ends of the potential difference detecting impedance element with a threshold value.